1. Field of the Invention
The present invention relates to an ink jet printing apparatus having a mechanism that applies the liquid to a print medium used for ink jet printing, for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials.
2. Description of the Related Art
In the field of ink jet printing apparatuses, those using a liquid applying mechanism are known. Japanese Patent Application Laid-open No. 2002-517341 describes an apparatus which uses a doctor blade contacting with a roller and in which the application liquid is collected between the blade and the roller so that the application liquid is applied to the roller as the roller rotates. As the roller rotates, the application liquid applied to the roller is transferred and applied to a support conveyed between this roller and another roller. Japanese Patent Application Laid-open No. 08-072227 (1996) similarly discloses a mechanism in an ink jet printing apparatus which applies a treatment liquid before printing which liquid insolubilizes dyes. In Embodiment 1 of this document, the treatment liquid in a replenishing tank is pumped by being attached to the rotating roller. At the same time, the treatment liquid pumped is applied to print paper.
However, in the configurations described in the above patent documents, an application liquid is applied or supplied to the surface of the rod bar or roller. However, the part of the rod bar or roller to which the application liquid is applied or supplied is open to or in communication with the air. Thus, disadvantageously, the application liquid may be evaporated or, for example, the application liquid may leak when the posture of the apparatus is changed. In particular, with an ink jet printing apparatus such as a printer, in view of, for example, the leakage of the liquid caused by a change in the posture of the apparatus, it is difficult to apply the applying mechanism described in the above documents to the apparatus if its size has been reduced.
In contrast, Japanese Patent Application Laid-open No. 08-058069 (1996) discloses a configuration that seals a part that applies or supplies inks, that is, application liquids, to a roller. The applying mechanism described in this document operates in a gravure printing apparatus to apply inks to a roller (applying roller) having the surface of which is formed with a pattern of a printing plate. This mechanism uses an ink chamber having two doctor blades arranged at two vertical positions along a peripheral surface of the roller and extending in a longitudinal direction of the roller and elastic members provided at the opposite sides of the two doctor blades. The chamber is contacted with the peripheral surface of the roller to form a liquid chamber between the ink chamber and the roller. Then, the roller is rotated to apply or supply the application liquid from the liquid chamber to the roller.
However, a sealing structure disclosed in Japanese Patent Application Laid-open No. 08-058069 (1996) may not have a sufficient sealing performance. More specifically, a roller in Japanese Patent Application Laid-open No. 08-058069 (1996) is formed with patterns for gravure printing, and thus the surface of the roller has irregularities. Consequently, ink may evaporate through this irregular portion and specifically ink may leak through the irregular portion at the time when the rotation of the roller is stopped.
Further, if the roller used in the gravure printing, which is disclosed in Japanese Patent Application Laid-open No. 08-058069 (1996), is employed as an applying roller for applying a liquid in an ink jet printing apparatus, the applying liquid is not applied uniformly due to the irregularities of the applying roller, and thus unevenness of application on a printing medium occurs. Then, if ink jet printing is performed to the printing medium on which the unevenness of application has occurred, the unevenness of the application affects an eventually obtained image to form the image having unevenness. Accordingly, it may be difficult to employ the applying structure in Japanese Patent Application Laid-open No. 08-058069 (1996) as the applying structure used in the ink jet printing apparatus, also in view of an image quality obtained.